Impacts of streamflow alteration on benthic macroinvertebrates by mini-hydro diversion in Sri Lanka

Abstract

Our study focused on quantifying the alterations of streamflow at a weir site due to the construction of a mini-hydropower plant in the Gurugoda Oya (Sri Lanka), and evaluating the spatial responses of benthic macroinvertebrates to altered flow regime. The HEC–HMS 3.5 model was applied to the Gurugoda Oya sub-catchment to generate streamflows for the time period 1991–2013. Pre-weir flows were compared to post-weir flows with 32 Indicators of Hydrologic Alteration using the range of variability approach (RVA). Concurrently, six study sites were established upstream and downstream of the weir, and benthic macroinvertebrates were sampled monthly from May to November 2013 (during the wet season). The key water physico-chemical parameters were also determined. RVA analysis showed that environmental flow was not maintained below the weir. The mean rate of non-attainment was ~ 45% suggesting a moderate level of hydrologic alteration. Benthic macroinvertebrate communities significantly differed between the study sites located above and below the weir, with a richness reduction due to water diversion. The spatial distribution of zoobenthic fauna was governed by water depth, dissolved oxygen content and volume flow rate. Our work provides first evidence on the effects of small hydropower on river ecosystem in a largely understudied region. Studies like this are important to setting-up adequate e-flows.

Food‐web energy fluxes, energy transfer efficiency, and diversity respond distinctively to pollution and water diversion in rivers

“…A decline in invertebrate density with flow reduction has been reported elsewhere (Martínez et al, 2020;Matthaei et al, 2010), but our study adds that this negative effect is more common in the polluted rivers, showing signs of an intensification of diversion effects with pollution. Similarly, other studies have shown that water diversion reduces local diversity (Munasinghe et al, 2021), due to the reduced habitat diversity (Cazaubon & Giudicelli, 1999). In our study, we demonstrate that α diversity is negatively affected by diversion only interactively with pollution, as the reduction was only obvious in the most polluted river.…”

“…These structures have multiple effects on ecosystems. The barriers themselves disturb the dispersion of aquatic organisms across the fluvial network (Jones et al., 2020), which affects community structure (Munasinghe et al., 2021). Additionally, water diversion driven by these infrastructures can modify environmental conditions through narrowing wetted channel, reducing flow velocity and water depth and altering water physico‐chemistry (Dewson et al., 2007a), which leads to changes in community abundance and diversity (Munasinghe et al., 2021).…”

Spatiotemporal Variation of Benthic Macroinvertebrates in Some Tropical Forest Streams of the Nyong Catchment (Cameroon)

“…These low abundance and richness of the community would be the consequence of the increase in speed and water depth. Reference [50] go further by saying that the increase in water flow leads to a reduction in taxonomic richness. Both spatially and temporally, no community has reached maximum diversity due to the constant renewal of taxa.…”

Understanding the role of natural and anthropogenic forcings in structuring the periphytic algal assemblages in a regulated river ecosystem

“…The method was repeated thrice in different places within a 10-m reach in the river to sample diverse velocity regimes and habitats until the 1 m 2 region had been covered. Hand-collected samples were also taken from individual boulders in the water 61 . The samples were kept in 100% ethanol for long-term storage until the identification process was finished.…”